Process for synthesizing diamond in a vapor phase

ABSTRACT

The present invention relates to a method for synthesizing diamond by chemical vapor deposition (CVD) process, and specifically a chemical deposition process which allows production of diamond of high purity and high crystallizability having various uses at low cost and at high speed. In the first method for the present invention, a mixture of oxygen gas and a carbon-containing compound gas and optionally an inert gas is introduced into a reaction vessel and a plasma is generated by use of an electromagnetic field, thereby producing diamond on a substrate placed in the vessel. In the second method of the present invention, a mixture containing at least one of fluorine gas, chlorine gas, a nitrogen oxide gas and sulfur dioxide gas, or a mixture of the gas mixture with oxygen gas and a carbon-containing compound gas, or a mixture thereof with an inert gas is introduced into a reaction vessel, and a plasma is generated by use of an electromagnetic field, thereby producing diamond on a base material placed in the vessel.

This application is a continuation of now abandoned application Ser. No.07/459,836 filed on Jan. 24, 1990.

TECHNICAL FIELD

The present invention relates to a process for synthesizing diamond bychemical vapor deposition process which allows production of diamondhaving high purity, high crystallizability and high versatility at lowcost and at high speed.

BACKGROUND ART

An artificial diamond was heretofore been synthesized underhigh-temperature, high-pressure thermodynamically equilibriumconditions. But recently a process for synthesizing diamond in a vaporphase has been developed.

In the vapor deposition process, hydrocarbon gas diluted with an overten times larger volume of hydrogen is excited by a plasma or a hotfilament to form a layer of diamond on a substrate in a reactionchamber.

As another prior art method, it is known to introduce a preheatedmaterial gas onto a heated substrate to pyrolytically decomposehydrocarbon to separate diamond (Japanese Patent No. 1272728).

Any prior art method for synthesizing diamond in a vapor phase requiresbasically a large amount of hydrogen, though it considers variousmethods for introducing neat to start a chemical reaction. Thus the costfor the material gas tends to be high. Moreover, hydrogen tends to betrapped in the diamond, thus lowering its purity and crystallizability.Also this will set limitations on the synthesis conditions of diamond,the speed of synthesis, the area of synthesis and the material of thesubstrate.

It is an object of the present invention to obviate these problems.

DISCLOSURE OF THE INVENTION

The present inventors have given consideration to various gas conditionsto find out that a stable plasma can be produced and diamond having agood crystallizability can be produced at a high speed over a large areaunder the following conditions where no hydrogen is used except for thehydrogen which may be contained in the compound gas. The conditions ofgas can be classified into two groups.

Namely, in the first method of the present invention, a mixture ofoxygen gas and a carbon-containing compound gas or a mixture furthercontaining an inert gas is introduced into a reaction vessel and aplasma is generated by an electromagnetic field, thereby producingdiamond on a substrate placed in the vessel.

In the second method of the present invention, a gas mixture of one ortwo or more of fluorine gas, chlorine gas, a nitrogen oxide gas and asulfur dioxide gas, or a mixture of the gas mixture with oxygen gas anda carbon-containing compound gas, or a mixture further containing aninert gas is introduced into a reaction vessel, and a plasma isgenerated by use of an electromagnetic field, thereby producing diamondon a substrate placed in the vessel.

With these methods, diamond develops uniformly and several times fasterthan with any prior art chemical vapor deposition (CVD) process, inwhich an expensive hydrogen gas is used in great amounts, and thediamond thus obtained contains no hydrogen over a large area (severaltens of square millimeters) and has a high purity and a highcrystallizability.

Either a direct current or alternating current electromagnetic field maybe used to produce a plasma. In the latter case, it should be ahigh-frequency wave or a microwave having a frequency of over 1 KH_(Z)for better controllability.

In order to produce a film of diamond of high purity and highcrystallizability while preventing the deposition of non-diamond carbon,the gases should be mixed in the first method so that the ratio betweenthe oxygen atoms and the carbon atoms in the material gas(oxygen/carbon) is 5-0.05 and preferably 2-0.1 and if the carboncompound contains hydrogen, the ratio among the oxygen, carbon andhydrogen atoms (oxygen/(carbon+hydrogen)) is 4-0.01 and preferably1-0.05.

If an inert gas is used in the first method, the ratio of atoms amongthe inert gas, oxygen and carbon (inert gas/(oxygen+carbon)) should be100-0 and preferably 20-0.02.

In the second method, the gases used should be mixed so that the ratioof atoms among fluorine (F), chlorine (Cl), oxygen (O) and carbon((F+Cl+O)/C) in the material gas is 5-0.05 and preferably 1.8-0.09. Ifthe carbon compound contains hydrogen, the ratio of atoms among fluorine(F), chlorine (Cl), oxygen (O), carbon (C) and hydrogen (H)(F+Cl+O)/(C+H) should be 4-0.01 and preferably 0.9-0.04.

If an inert gas is used in the second method, the ratio of atoms amongthe inert gas (X), fluorine (F), chlorine (Cl), oxygen (O), nitrogen(N), sulfur (S), and carbon (C) (X/(F+Cl+O+C) should be 100-0 andpreferably 20-0.01.

The use of inert gas is highly desirable in either of the first andsecond methods because it not only makes it possible to produce a plasmain a wide pressure range and accelerate and developing speed, but alsofacilitates coating over a wide area.

The inert gas used in the present invention may be helium (He), neon(Ne), argen (Ar), kripton (Kr) or xenon (Xe) or a combination thereof.In view of the mass-productivity and production cost of diamond, argongas is the most desirable because it is inexpensive.

The carbon-containing compound gas may be methane, ethane, acetylene,propane, natural gas, carbon monoxide or carbon dioxide in the form of agas or an organic compound containing a small amount of oxygen,nitrogenor sulfur in its alcohol molecules or the like.

The aforementioned and other preferred modes of the present inventionare briefly described below.

(1) If an alternating current electromagnetic field is used to generatea plasma, it should be a high-frequency wave or a microwave having afrequency of 1 KH_(Z) or more and preferably be a microwave having afrequency of 300 MH_(Z) or more.

(2) The carbon-containing compound gas to be mixed with other gasesshould be one or two or more selected from an aliphatic hydrocarbon, anaromatic hydrocarbon, alcohol and ketone.

(3) The electric power for the generation of a plasma should be 1 W/cm³or more and the pressure in the reaction chamber should be 5-760 Torr.

(4) The flow rate of the gas mixture at the reaction portion for theproduction of diamond should be 0.1 cm/sec or higher.

(5) In the first method the gases should be mixed so that the ratio ofatoms in the material gases will be:

5-0.05 and preferably 2-0.1 in the oxygen/carbon ratio;

4-0.01 and preferably 1-0.05 in the oxygen/(carbon+hydrogen) ratio, ifthe carbon-containing compound gas contains hydrogen.

In the second method, the gases should be mixed so that the ratio ofatoms in the material gases will be 5-0.05 and preferably 1.8-0.09 inthe (F+Cl+O)/C ratio; and

If the carbon-containing compound gas contains hydrogen, it will be4-0.01 and preferably 0.9-0.04 in the (F+Cl+O)/(C+H) ratio.

(6) If an inert gas is used,

the ratio of atoms in the first method should be 100-0 and preferably20-0.02 in the inert gas/(oxygen+carbon) ratio; and

the ratio of atoms in the second method should be 100-0 and preferably20-0.01 in the X (insert gas)/(F+Cl+O+C) ratio.

According to the present invention, such manufacturing conditions as thetemperature of the substrate (300°-1200° C.), the pressure in thereaction tube, the ratio of mixture of gases, and the flow rate of gascan be readily controlled. Also, the use of an oxygen plasma makes itpossible to form a diamond coating even on a substrate having athree-dimensional structure,which was heretofore been difficult.Further, since no hydrogen is used, a diamond coating can be formed evenon a substrate which is liable to get brittle under the influence ofhydrogen.

By suitably setting the manufacturing conditions, diamond of a largegrain size, over several hundred microns in diameter, can be developedat a high speed. A microwave is the most preferable for the formation ofplasma in the production of diamond in a vapor phase. Electrodes shouldpreferably not be provided in the reaction vessel in order to stabilizethe plasma. The temperature of the substrate may be controlled bycooling it or by use of a heating means. Such means may be made of aninsulating material in order to prevent the plasma from being disturbedif it is placed in the reaction vessel.

The substrate used may be a ceramic such as silicon, Si₃ N₄, SiC, BN, B₄C and AlN, or a metal having a high melting point such as molybdenum,tungsten, tantalum and niobium. If the temperature of the substrate islow, copper or aluminum or their alloy or cemented carbide may be used.If the reaction takes place in an atmosphere containing oxygen, it isnecessary to control the partial pressure with hydrogen which isproduced by decomposition. Further the emission spectral analysisrevealed that the plasma generated under the conditions according to thepresent invention differs from the plasma generated by the prior artmethod in which hydrogen gas is used as a main material gas, in that theformer is relatively low in the strength of the hydrogen continuous bandand high in the strength of hydrogen atoms such as H (X). This suggeststhat the decomposition of the material gas takes place more efficientlyin the method according to the present invention than in the prior artmethod (FIG. 8).

In the prior art method, the deposition of diamond occurs under a lowdegree of saturation of the carbon-containing compound gas, i.e. whileits concentration with respect to the hydrogen gas is as low as severalper cent by volume (0.8-2.0 per cent by volume), whereas in the methodaccording to the present invention, it occurs while the degree ofsaturation is several hundred times higher than with the prior artmethod. It is presumed that this makes it possible to deposit film ofdiamond which has less defects and is of high quality.

According to the present invention, because oxygen is used (in the firstmethod) for the synthesis of diamond by the plasma CVD process, insteadof using a large amount of hydrogen as with the prior art method, and inthe second method, a mixture containing one or more of fluorine gas,chlorine gas, nitrogen oxide gas, and sulfur dioxide gas, or the mixturefurther containing oxygen gas is used, the following effects can beobtained.

(1) Since oxygen used in the first method is cheaper than hydrogen, theproduction cost can be reduced.

(2) A diamond coating can be formed even on a substrate which is liableto get brittle, such as titanium.

(3) A film of diamond of high purity and high crystallizabilitycontaining no hydrogen is obtainable.

(4) By suitably setting the manufacturing conditions, diamond can beselectively developed in the form of either grains or a film at a speedof more than 100 microns/hour.

(5) A diamond coating can be formed not only on a substrate having acomplex shape but also over a large area.

(6) In the method where an inert gas is used, a plasma can be generatedwithin a wide pressure range. This serves to further increase thedeveloping speed of diamond as well as the area of development.

The above-described effects suggest that the method according to thepresent invention can be used for the production of a diamond heat sinkand diamond abrasive grains which have heretofore been producedexclusively by the high-pressure process. The method of the presentinvention can also be used for the production of diamond in the form ofa film no more than several microns thick and a substrate several tensof microns thick and which can be used in a field where the film isrequired to have a high heat conductivity, a low inductivity, a highlight transmittance, a high specific elastic modulus, a high strengthand a high resistance to wear.

This method can be carried out with a conventional device without thenecessity of changing the abovementioned manufacturing steps or addingextra steps thereto. This will permit a stable operation and ensure alow facility cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are schematic views of plasma CVD devices applicable to themethod according to the present invention.

FIGS. 5 to 7 are graphs showing a Raman spectrum, a penetrating spectrumand cathode luminescence spectrums for each specimen shown in Table 1.

FIG. 8 is a graph showing an emission spectrum of the plasma.

BEST MODE FOR EMBODYING THE INVENTION

FIGS. 1 to 4 show schematic views of devices for synthesizing diamondwhich are applicable to the present invention.

FIG. 1 shows a microwave plasma CVD device (hereinafter referred to asμ-PCVD). FIG. 2 shows a high-frequency plasma CVD device (hereinafterreferred to as RF-PCVD). FIG. 3 shows a direct current plasma CVD device(hereinafter referred to as DC-PCVD). FIG. 4 shows a high-frequencyhigh-temperature plasma CVD device (hereinafter referred to asRF-HPVCD). Any of these devices can be used in the present invention. Inthe drawings, numeral 1 shows a substrate, 2 is a reaction silica tube,3 is a vacuum discharge port, 4 is an inlet for material gas, 5 is aplasma generated, 6 is a magnetron, 7 is a waveguide, 8 is a plunger foradjusting the position of plasma, 9 is an RF power source, 10 is a DCpower source, 11 is a table for supporting the substrate, 12 is aninsulating seal, and 13 is a cathode. The silica tube shown in FIG. 4can be cooled.

Next, description will be made of the examples according to the presentinvention and comparative examples, in which the above-described fourdevices were used.

EXPERIMENT 1 Comparison between the first method and a prior art

The devices used and other manufacturing conditions are shown in Tables1 and 2. The substrates used both in the Examples and the comparativeexamples were single-crystal silica wafers of 2 inch (50.8 mm indiameter) finished by use of #5000 diamond powder. A material gas wasintroduced with the substrate held in the reaction silica tube 2 and aplasma was generated by a plasma generator under the pressure of 1 Torr.The pressure in the tube was increased quickly to the pressure levelsshown in Table 1 and held at those levels to develop and synthesizediamond on the substrate for the periods shown in Table 1. The surfacetemperature of the substrate was measured by use of an optical pyrometerby momentarily interrupting the generation of plasma.

Tables 1 and 2 show the results of surface observation of each of thediamond specimens produced under the respective conditions by use of ascanning type electron microscope, measurement of film thickness, X-rayanalysis and evaluation of crystallizability by the Raman scatteringspectrum process.

FIGS. 5to 7 show a Raman spectrum, a penetrating spectrum in theultraviolet and visible ranges, and cathode luminescence spectrumsgenerated by irradiation of electron beams for the specimen No. 2 inTable 1, respectively. FIG. 5 shows that the diamond film thus producedhas an excellent crystallizability.

FIG. 6 shows that it has an absorption end in the region of 225 nm inwave number and has a high transmittance from the ultraviolet region tothe infrared region. Thus it is believed that such a material can beadvantageously used for window material. In FIG. 7, the curve (a) showsa cathode luminescence spectrum of a prior art specimen (sample No. 13in Table 2) made by use of hydrogen and curve (b) shows a spectrum of aspecimen (sample No. 2 in Table 1) made by use of oxygen. Ti/Mo/Auelectrodes were metallized to measure the electrical resistance. Theresistance measured was over 10¹² ohms, which reveals that theresistance can be kept stably at a very high level even after themetallization of diamond.

EXPERIMENT 2 Comparison between the second method and a prior art method

Tables 3 and 4 show the devices used and the manufacturing conditions inthis experiment. In this experiment, diamond was developed andsynthesized on the same single-crystal silica wafer as that used in theexperiment 1 under the same conditions as the experiment 1. Thespecimens thus produced were evaluated in the same manner as with theexperiment 1.

In the tables, "Dia" indicates diamond, "gr" does graphite, and "a-c"does amorphous carbon. In Table 3, F indicates fluorine, Cl doeschlorine, O does oxygen, C does carbon and X does at least one inertgas.

    __________________________________________________________________________    Present Invention                                                             Manufacturing Conditions                                                                 Gas used                                Elec. Substrate            Sample                                                                            Mfg.   flow rate    Pressure                                                                           Time           Inert gas/                                                                           Power temp.                No. method (SCCM)       (Torr)                                                                             (h)  O/C O/(C + H)                                                                           (O + C)                                                                              (W)   (°C.)         __________________________________________________________________________    1   μ-PCVD                                                                            O.sub.2  CH.sub.4                                                                           80  10   2   0.4   --      500  850                             100      100                                                       2   μ-PCVD                                                                            O.sub.2  CH.sub.4                                                                          100  5    1.3 0.27  --      600  800                             240      360                                                       3   μ-PCVD                                                                            O.sub.2  C.sub.2 H.sub.2                                                                   100  2    0.67                                                                              0.33  --      800  900                             400      600                                                       4   μ-PCVD                                                                            O.sub.2  CO  150  1    1.25                                                                              --    --      400  880                             50       400                                                       5   μ-PCVD                                                                            O.sub.2                                                                           Ar   CO.sub.2                                                                          400  5    2.25                                                                              --    0.77   1000  920                             100 2000 800                                                       6   μ-PCVD                                                                            O.sub.2                                                                           He   C.sub.3 H.sub.8                                                                   600  10   0.27                                                                              0.073 0.026  1500  890                             200 50   500                                                       7   RF-PCVD                                                                              O.sub.2  C.sub.2 H.sub.2                                                                    5   10   0.75                                                                              0.375 --     1000  800                             300      400                                                       8   DC-PCVD                                                                              O.sub.2                                                                           Ar   CH.sub.4                                                                          200  10   1.3 0.27  0.29   1000  950                             100 100  150                                                       9   RF-HPCVD                                                                             O.sub.2                                                                           Ar   C.sub.2 H.sub.4                                                                   200  1    1.0 0.33  2.5    4500  950                             2000                                                                              20000                                                                              2000                                                      10  μ-PCVD                                                                            O.sub.2  CH.sub.4                                                                          100  1    0.1 0.02  --     1500  900                             50       1000                                                      11  μ-PCVD                                                                            O.sub.2                                                                           Ar   CH.sub.4                                                                          400  2    20  4     0.048   800  850                             1000                                                                              100  100                                                       12  RF-PCVD                                                                              O.sub.2                                                                           Ne   C.sub.2 H.sub.2                                                                    80  10   1   0.5   50     1000  850                             1   800  1                                                         13  μ-PCVD                                                                            O.sub.2  CH.sub.4                                                                           80  1    1.3 0.27  --      200  400                             240      360                                                       14  μ-PCVD                                                                            O.sub.2                                                                           Ar   CH.sub.4                                                                           80  1    1.3 0.27  0.29    100  350                             100 100  150                                                       __________________________________________________________________________    Present Invention                                                             Results                                                                       Sample                                                                        No. Deposition speed (μm/h)                                                                Film thickness (μm)                                                                  Separated area (mm.sup.2)                                                                Line diffraction                                                                      Raman spectroscope                                                                      Remarks                __________________________________________________________________________    1   10          100       1950       Dia     Dia                              2   40          200       1800       Dia     Dia                              3   100         200        800       Dia     Dia                              4   300         300        600       Dia     Dia                              5   200         1000       400       Dia     Dia                              6   500         5000       500       Dia     Dia                              7   5           50        1600       Dia     Dia                              8   200         2000       80        Dia     Dia                              9   700         700        100       Dia     Dia                              10  10          10        1800       Dia     Dia       Reaction tube                                               +gr     +gr       dirty poor                                                          +a-c      crystalizability       11  0.01        0.02       300       Dia     Dia       Slow growth            12  0.1         1         1900       Dia     +Dia      Poor                                                        +gr     +gr       crystalizability                                                    +a-c                             13  2           2          800       Dia     Dia       Slow growth            14  1           1          800       Dia     Dia       Slow                   __________________________________________________________________________                                                           growth             

                                      TABLE 2                                     __________________________________________________________________________    Comparative Examples                                                          Manufacturing Conditions                                                                 Gas used                                  Elec.                                                                              Substrate           Sample                                                                            Mfg.   flow rate         Pressure                                                                           Time         Inert gas/                                                                          Power                                                                              temp.               No. method (SCCM)            (Torr)                                                                             (h) O/C                                                                              O/(C + H)                                                                           (O + C)                                                                             (W)  (°C.)        __________________________________________________________________________    13  μ-PCVD                                                                            H.sub.2      CH.sub.4                                                                           40   1   -- --    --     400 900                            200          5                                                     14  μ-PCVD                                                                            H.sub.2 C.sub.2 H.sub.2                                                                    O.sub.2                                                                            50   10  -- --    --     500 850                            50      0.25 0.1                                                   15  μ-PCVD                                                                            H.sub.2                                                                           Ar  C.sub.2 H.sub.5 OH                                                                 H.sub.2 O                                                                          80   4   -- --    --     800 880                            100 10  1000 4                                                     16  RF-PCVD                                                                              H.sub.2                                                                           He       CH.sub.4                                                                            1   10  -- --    --    1000 800                            100 100      2                                                     17  DG-PCVD                                                                              H.sub.2      C.sub.2 H.sub.5 OH                                                                 200  2   -- --    --    1200 920                            100          100                                                   18  RF-HPCVD                                                                             H.sub.2                                                                           Ar       CH.sub.4                                                                           200  0.5 -- --    --    5000 900                            8000                                                                              10000    200                                                   __________________________________________________________________________    Comparative Examples                                                          Results                                                                       Sample                                                                        No. Deposition speed (μm/h)                                                                Film thickness (μm)                                                                  Separated area (mm.sup.2)                                                                Line diffraction                                                                      Raman spectroscope                                                                      Remarks                __________________________________________________________________________    13  1           1         800        Dia     Dia                                                                           +a-c                             14  0.5         5         400        Dia     Dia                              15  1.5         6         300        gr      gr                               16  0.1         1         600        Dia     Dia                                                                   +gr     +gr                                                                           +a-c                             17  20          40         15        Dia     Dia                                                                   +gr     +gr                                                                           +a-c                             18  80          40         10        Dia     Dia       Plasma                 __________________________________________________________________________                                                           unstable           

                                      TABLE 3                                     __________________________________________________________________________    Present Invention                                                             Manufacturing Conditions                                                                                                           Elec.                                                                              Substrate           Sample                                                                            Mfg.   Gas used flow rate                                                                        Pressure                                                                           Time                                                                             (F + Cl +                                                                           (F + Cl + O)/                                                                         X/(F +  power                                                                              temp                No. method (SCCM)      (Torr)                                                                             (h)                                                                              O)/C  (C + H) Cl + O + C)                                                                           (W)  (°C.)        __________________________________________________________________________    1   μ-PCVD                                                                            F.sub.2  CH.sub.4                                                                          90  10 1     0.2     --       480 870                            50       100                                                       2   μ-PCVD                                                                            F.sub.2  CH.sub.4                                                                          80  5  0.83  0.17    --       550 820                            150      360                                                       3   μ-PCVD                                                                            F.sub.2  C.sub.2 H.sub.2                                                                  180  2  0.53  0.27    --       650 880                            320      600                                                       4   μ-PCVD                                                                            F.sub.2                                                                          NO    CO 150  10 1.13  --      --       500 900                            20 10    400                                                       5   μ-PCVD                                                                            Cl.sub.2                                                                         Ar    CO.sub.2                                                                         400  5  2.01  --      0.042   1100 925                            5  100   800                                                       6   μ-PCVD                                                                            F.sub.2                                                                          Cl.sub.2                                                                         He C.sub.3 H.sub.8                                                                  600  10 0.27  0.073   0.26    1600 900                            100                                                                              100                                                                              500                                                                              500                                                       7   RF-PCVD                                                                              F.sub.2  C.sub.2 H.sub.2                                                                   5   1  0.75  0.375   --      1200 820                            300      400                                                       8   DC-PCVD                                                                              F.sub.2                                                                          Ne    CH.sub.4                                                                         200  10 1.3   0.27    0.29    1000 950                            100                                                                              100   150                                                       9   RF-HPCVD                                                                             Cl.sub.2                                                                         Ar    C.sub.2 H.sub.2                                                                  200  1  0.5   0.5     2.5     5500 950                            2000                                                                             2000  2000                                                      10  μ-PCVD                                                                            F.sub.2  CH.sub.4                                                                         120  1  0.1   0.02    --      2000 920                            50       1000                                                      11  μ-PCVD                                                                            F.sub.2                                                                          Cl.sub.2                                                                         Ar CH.sub.4                                                                         400  2  20    4       0.048    900 900                            500                                                                              500                                                                              100                                                                              100                                                       12  RF-PCVD                                                                              Cl.sub.2                                                                         Ar He C.sub.2 H.sub.2                                                                   80  10 1     0.5     50      1000 800                            1  600                                                                              200                                                                              1                                                         __________________________________________________________________________    Present Invention                                                             Results                                                                       Sample                                                                        No. Deposition speed (μm/h)                                                                Film thickness (μm)                                                                  Separated area (mm.sup.2)                                                                Line diffraction                                                                      Raman spectroscope                                                                      Remarks                __________________________________________________________________________    1   4           40        1940       Dia     Dia                              2   20          100       1600       Dia     Dia                              3   80          160       1000       Dia     Dia                              4   40          400        550       Dia     Dia                              5   180         900        500       Dia     Dia                              6   520         5200       400       Dia     Dia                              7   3           3         1700       Dia     Dia                              8   180         1800       85        Dia     Dia                              9   650         650        90        Dia     Dia                              10  8           8         1950       Dia     dia       Reaction tube                                               +gr     +gr       dirty Poor                                                          +a-c      crystallizability      11  0.007       0.014      300       Dia     Dia       Poor growth            12  0.08        0.8       1600       Dia     +Dia      Poor                                                        +gr     +gr       crystallizability                                                   +a-c                             __________________________________________________________________________

    __________________________________________________________________________    Comparative Examples                                                          Manufacturing Conditions                                                                                                            Elec.                                                                             Substrate           Sample                                                                            Mfg. Gas used flow rate                                                                             Pressure                                                                           Time                                                                             (F + Cl +                                                                           (F + Cl +                                                                            X/(F + Cl                                                                            power                                                                             temp                No. method                                                                             (SCCM)           (Torr)                                                                             (h)                                                                              O)/C  O)/(C + H)                                                                           O + C) (W) (°C.)        __________________________________________________________________________    13  μ-                                                                              H.sub.2     CH.sub.4                                                                           40   1  --    --     --      400                                                                              900                     PCVD 200         5                                                        14  μ-                                                                              H.sub.2                                                                              C.sub.2 H.sub.2                                                                    O.sub.2                                                                            50   10 --    --     --      500                                                                              850                     PCVD 50     0.25 0.1                                                      15  μ-                                                                              H.sub.2                                                                          Ar  C.sub.2 H.sub.5 OH                                                                 H.sub.2 O                                                                          80   4  --    --     --      800                                                                              880                     PCVD 100                                                                              10  1000 4                                                        16  RF-  H.sub.2                                                                          He       CH.sub.4                                                                            1   10 --    --     --     1000                                                                              800                     PCVD 100                                                                              100      2                                                        17  DC-  H.sub. 2    C.sub.2 H.sub.5 OH                                                                 200  2  --    --     --     1200                                                                              920                     PCVD 100         100                                                      18  RF-  H.sub.2                                                                          Ar       CH.sub.4                                                                           200  0.5                                                                              --    --     --     5000                                                                              900                     HPCVD                                                                              8000                                                                             10000    200                                                      __________________________________________________________________________    Comparative Examples                                                          Results                                                                       Sample                                                                        No. Deposition speed (μm/h)                                                                Film thickness (μm)                                                                  Separated area (mm.sup.2)                                                                Line diffraction                                                                      Raman spectroscope                                                                      Remarks                __________________________________________________________________________    13  1           1         800        Dia     Dia                                                                           +a-c                             14  0.5         5         400        Dia     Dia                              15  1.5         6         300        gr      gr                               16  0.1         1         600        Dia     Dia                                                                   +gr     +gr                                                                           +a-c                             17  20          40         15        Dia     Dia                                                                   +gr     +gr                                                                           +a-c                             18  80          40         10        Dia     Dia       Plasma                 __________________________________________________________________________                                                           unstable           

What is claimed is:
 1. A method for synthesizing diamond by vapor phasedeposition, consisting essentially of the steps of introducing a gasmixture of at least one of fluorine gas and chlorine gas and a gaseouscompound containing carbon into a reaction vessel, said gas mixture notcontaining hydrogen gas,keeping the pressure in said reaction vessel at5-760 Torr, and generating a plasma in said vessel by means of a directcurrent or alternating current electromagnetic field, thereby producingdiamond on a substrate held in said vessel.